What characterizes a pressure ulcer?

A pressure ulcer is chiefly characterized by localized injury that occurs due to prolonged pressure on the skin and underlying tissues. This pressure inhibits blood flow, leading to ischemia and tissue death if it is not relieved. Pressure ulcers typically develop over bony prominences where the skin is particularly vulnerable, such as the heels, sacrum, and elbows.

The mechanism behind the formation of pressure ulcers involves the sustained compression of blood vessels, which compromises oxygen and nutrient delivery to the tissues. Over time, the affected areas may progress through stages of severity, from non-blanchable erythema to full-thickness tissue loss.

Other options describe different types of injuries but do not apply to pressure ulcers. For instance, friction injuries involve the skin being rubbed against a surface, which is distinct from the effects of prolonged pressure. Similarly, injuries from thermal burns or chemical exposure are unrelated to the primary cause of pressure ulcers, which is sustained pressure rather than mechanical or chemical damage. Thus, emphasizing the specific nature of tissue injury due to prolonged pressure highlights the defining feature of pressure ulcers.